crossfitter wrote:It's actually not wrong at all. Weight is simply force due to gravity, and the equation deuces posted is perfectly accurate (if somewhat simplified).

Thanks, Crossfitta.

I am a very simple Mensan.

I really like to learn, so another question for the Physicians among us:

The point I find interesting, is that acceleration, or in this case mostly deceleration, loads the front tire of the bike disproportionately. So, in my simple mind, this greater FORCE, applied over a smaller area (the front tire) coupled with excessive shear (mentioned by Crossfitta) means there is a lot of destructive force applied to the tundra. Seemingly different in some way from the way force is applied by a hiker at least in terms of scale.

Not that I have an issue with bikers.

Thoughts?

EDIT: Funny pic of Tebow. I like Tebow even though he's religulous. John Elway is currently the biggest problem with Denver Broncos football. That dude's massive ego needs to be retired.

If I only had a dollar for every claimed MENSA member on this site over the years... Seems to me the real MENSA members I've ever met don't really brag about it; they just are. I'll give you the benefit of not knowing you but for the number of people who have claimed MENSA on this site versus the overall 14er population, this group of climbers is a worldwide statistical anomaly.

And normal force IS definitely equal to the weight of an object, before movement (acceleration) is applied; then they are no longer equal.

Just stay on the trail people, unless there is no trail and then use your best judgment as to the path towards your destination.

Isn't a bike moving when used as intended? I think my comment/question is a fair one. I like learning new stuff after all. I wouldn't want to remain static, would I?

Didn't mean to get your Mensa up, Bill. I've only been a member for a short time and sometimes forget the rules. Sorry.

Well the discussion is all over the place anyway, from the initial "stay on the trail" discussion to the static PSI discussion and ground pressure. When it comes to real trail damage, sure, practical factors like the way bikes are ridden or braked or pushed uphill by average versus skilled vs. unskilled riders comes into play...as does the sheer number of hikers vs. cyclists...but I thought we were focused on minutiae.

Sorry to rehash topics that so many have covered already, but I couldn't resist.

As far as PSI goes, certainly an inflated tire acts to distribute pressure over area. If you inflate your tire to a reasonable level while weighted, the tire deforms and the weight is distributed close-to-evenly over the area. This lowers the maximum PSI inflicted on the ground and reduces road damage. Of course if the weight* rises (most likely due to dropping down a foot, if you're riding down a mountain) the forces all rise temporarily and the PSI will increase inside the tire just as the PSI from tire to ground increases, but the distribution effect still acts (imperfectly no doubt) to lower the maximum forces. As you raise the PSI within your tire, it deforms less and there is less weight redistribution. As you lower the PSI, the weight will be more and more distributed, but your tire will also wear faster and eventually your wheel rims will just be resting on the ground. No math should be needed to understand this process; think of it like deforming a balloon in your hands.

But what I'm not sure on is why this matters all that much. Most of the time the force of a bike is straight down (no skidding) - and this surely does quite low damage to the ground. What tears up ground is friction, from a bike skidding or from a hiker's foot slipping slightly. This (along with water flow) is why the steeper trails erode so much faster, and why there's so much faster erosion in wet weather. If a bike does skid, the distributed force from the tires is going to be a lot less distributed; likewise if a hiker slips it's often with all the weight on the toes.

* By weight, I mean force, specifically the downward force of the bike on the ground. I realize this is technically inaccurate since weight/force is the force of gravity on the object which would indeed be constant. But the force between ground and bike is going to vary if any bounce is present.

Dex wrote:You are equating internal psi with external psi on the ground.

Where is Bean2 when you need him.

Internal PSI = External PSI. Simple physics, opposite and equal forces. Bean is correct in the example he uses. The pressure in a tire does not change due to load.

Following this line of reasoning I can conclude that the best way to reduce trail damage as possible is to let all the air out of my tires. Afterall, if "Internal PSI = External PSI", then 0 PSI in the tires means 0 PSI exerted by the bike upon the surface of the trail.

Right?

I am unable to walk away from the mountain without climbing it. An unclimbed mountain tugs at my consciousness with the eternal weight of time itself. Until I've pressed my face into it's alpine winds, hugged it's ancient granite walls, and put it's weathered summit beneath my heal I'm unable to resist it's attraction.Knowing nature gives the mountain more time than she gives us adds urgency to the obsession. As has been said before; the mountain doesn't care.